1. Field of the Invention
The invention relates to a sealing arrangement comprising a preferably one-piece, peripheral, rubber-like sealing material for sealing the sealing space in a rotary joint.
2. Description of the Prior Art
Seals having an inner ring and an outer ring currently available commercially and in use for sealing rotary joints and slewing bearings, differ widely in shape and design, even though the uses are often very similar. The objective is always to protect the rotary joint or slew drive, or, in general, the slewing bearing or rolling bearing, reliably against external influences, for example moisture, wind-borne sand, contaminants or dirt, foreign bodies, etc.
A practical sealing arrangement must also ensure resistance to the internal pressure of lubricant in the bearing. The seal should satisfy the requirements for preventing foreign bodies from getting into the bearing structure of the joint. At the same time, the seal must support the aim of keeping the lubricant inside the bearing, or allowing only small and defined quantities of it to escape from the assembly, as a whole. It therefore must have a reasonable ability to withstand the internal pressure of the bearing caused by the lubricant.
It is the current state of the art that the lubricants, or lubricating agents, used in rotary joints, slewing bearings, and slew drives, come into contact with the seal material.
It is also the current state of the art that the seals that are available commercially and are in use are vulcanizable and can be made by all the established methods for producing seal geometries from elastic, rubber-like materials, for example FPM, Viton, NBR, ECO, HNBR, and the like.
Ordinary sealing arrangements according to the state of the art have in common that they are usually either one-piece or multi-piece, i.e., they consist of at least one sealing component.
Very frequently, various annular sealing strips are inserted in the rotary joint, or are fastened in one or more plunge cuts or grooves in the solid material of the rotary joint, or on the slew drive, such that fixation occurs. The fixation is brought about in such cases by inserting the elastic seal material into a groove present in the (metallic) solid material of the assembly to be sealed. This groove is often made by chip-producing machining as a consequence of so-called “plunge-cut turning” during the production of the rotary joint or bearing.
It is often the case that a plurality of such grooves, or plunge cuts, are present in the overall assembly to be sealed. There are frequently at least exactly as many of these grooves as there are elastic sealing strips to be inserted and fixed in the assembly.
The fixation of the sealing strips, or sealing profiles, in the aforesaid grooves, or plunge cuts, is normally accomplished, on the one hand, by means of a form lock, since the elastic springs or lips of the sealing strips, or sealing profiles that are inserted in the grooves, often have a barb-shaped profile geometry or geometries, and also, on the other hand, by virtue of the fact that when the rotary joint is operated as intended, any deformation forces act on the seals generally perpendicularly to the insertion axis of the groove, and thus not in the direction in which the profile geometry, or geometries, of the sealing ring would be pulled out of the groove or plunge cut.
Moreover, the fixation of the sealing arrangement in the metallic solid material can usually be cancelled by the application of force. This means that by applying a given pulling force, which must act in the opposite direction from the force exerted to insert the seal into the solid material, the practitioner or skilled person can disengage the inserted seal from the metallic assembly (rotary joint, slew drive or, in general: slewing bearing).
Due primarily to this fact, according to the known state of the art, that portion of the sealing profiles which is to be inserted in a groove, or plunge cut, is configured as barb-shaped.
However, it is the case according to the known state of the art that each seal is fixed in the solid material of the rotary joint, or slewing bearing, at at least one location, so as not to depart from the fixed position when operated as intended. The sealing effect is respectably good, as a rule.
It is often seen at present for an elastic portion of the described profile geometry, or geometries, of the sealing arrangement to be fixed to the one rotating part of a rotary joint and for another portion of the same sealing arrangement to be fixed to the other rotating part of the rotary joint, and for the sealing effect to be created by the interaction of all the sealing components involved in the assembly as a whole (which are, for example, a first elastic seal, an additional high-grade steel band, an additional tension spring band and a second elastic seal, plus any third elastic sealing components that may desired).
For example, EP 1 920 176 B1, based on DE 10 2005 041720 A1, describes a successful arrangement of this kind for sealing a rotating joint in which the sealing arrangement consists of many individual components, each extending annularly, and in which the sealing ring is fixed in the aforesaid manner to one of the rotating parts. As is readily apparent in that document, the particular groove or plunge cut for fixing the seal in the bearing components can be disposed either in the same direction as the sealing gap or perpendicular to the sealing gap.
DE 103 09 383 A1 also pertains to an annularly extending peripheral sealing ring that is fixed to one of the rotating parts in the aforesaid manner. In this case, the barb-shaped portion is pressed into a groove or a plunge cut disposed, perpendicular to the sealing gap, in one of the rotating bearing components. According to this solution, a second peripheral element is needed for additional fixation of this seal in the horizontal direction.
DE 10 2006 053 832 A1 should also be cited in this connection. There, the subject matter is a one-piece peripheral sealing element in which, as noted above, a portion of the seal is pressed into a groove, or plunge cut, arranged in one of the rotating bearing components so as to be perpendicular to the sealing gap.
According to the current state of the art, therefore, sealing arrangements are very often encountered in the field in which the plunge cut, or the groove, is located either in the gap to be sealed between two mutually rotatable elements, specifically so that the groove or plunge cut is perpendicular to the gap, such as, for example, the small gap seal located on the bearing side that is disclosed in DE 10 2005 041 720 A1; that seal, however, is not able to develop a sealing effect on its own, but for that reason is instead used only in an auxiliary capacity and in conjunction with other, larger sealing arrangements.
Alternatively, in the current state of the art, such one-piece peripheral refinements of sealing arrangements can be encountered in the field in which the plunge cut or groove lies in the direction of the gap. In particular, German applications DE 10 2008 025 725 A1 and DE 10 2008 027 890 A1 relate to such sealing systems, in which a groove or, better, a plunge cut, lies in the same direction as the gap. Here again, the geometries of the sealing profiles are always sharply asymmetrical and rest against the opposite rotating part or the opposite rotating bearing component at several points.
WO 2010/043249 A1, which also describes a one-piece peripheral sealing component, is also very striking. Here again, it is quite clear that a barb-shaped portion is present and is pressed into the plunge cut disposed in the direction of the sealing gap.
It is clearly apparent from an examination of WO 2010/043249 A1, as well as DE 10 2008 025 725 A1 and DE 10 2008 027 890 A1, that each of these solutions includes upper and lower sealing lips which rest against the opposite bearing components in order to seal there, and which, upon displacement of the bearing, can deform upwardly or downwardly toward each other to compensate for bearing play, the upper sealing lip then being pushed upwardly and the lower sealing lip being pushed downwardly. In all cases, however, this upper and lower sealing lip not only provides a sealing effect, but additionally serves to fix the particular bearing assembly against being pushed out axially. Nevertheless, this fixation is present only if the bearing play (i.e., the size of the gap between the inner and outer rings) is not too great. The greater the gap size, the greater the degree to which the strength of the fixation of the seal in the plunge cut depends on how well the barbs remain in place in the plunge cut. This is disadvantageous, particularly if the internal pressure in the bearing increases sharply.
Common to all of the aforesaid solutions is the fact that they can be used, for example, to seal rotary joints employed in wind power installations—for example, to seal rotary joints in the azimuth bearing, tower bearing, as a rotor bearing, or also as a bearing for adjusting the rotor blades. Other types of use in this area of application is also conceivable, however.
In recent years, it has been increasingly desired in practice for such sealing arrangements chiefly to have a profile geometry, or geometries, that can be inserted between the two rotating parts, that provide good fixation, and that achieve a very good and, above all, long-lasting sealing effect. A major problem with many of the aforesaid sealing arrangements is that their intrinsically good sealing effect stands or falls according to how stably, or well, the seal remains in place in the installed position. Many of the current sealing systems fail during operation because the sealing arrangement is pushed out of the installed position as a result of too high an internal pressure in the bearing (due to too much lubricant, for example).
It is always highly disadvantageous in practice if the seals drop out of the rotary joint, since the whole installation breaks down as a result. In particular, the barb-shaped portion of the seal will occasionally, or after deforming, drop out of the plunge cut of the rotary joint, or will be pushed out axially due to excessive lubricant pressure. True, all of the above-cited solutions are designed to last for many years under severe weather conditions and to seal reliably, nonetheless. But practical experience has shown that none of the aforesaid seals constitutes a simple sealing solution, or that due to their inadequate fixing capabilities, the sealing solutions lose their positional stability in the seal, or are expelled from it outright after some periods of operation.
Particularly in the case of multi-piece solutions, additional complexities arise during installation (since a number of individual parts have to be installed). This costs time and money in practice.
In particular, the last three technical documents cited, WO 2010/043249 A1, DE 10 2008 025 725 A1 and DE 10 2008 027 890 A1, are very similar in geometry and therefore present the problem that they run the risk of losing their positional stability during operation, that is, they may be pushed out of the bearing while the installation is operating, due to excessive deformation or too high an internal pressure in the bearing, transmitted outward through the sealing space or sealing gap. Even if this process occurs insidiously, after a given time it will result in a breakdown of the rotary joint to be sealed, or of the associated installation, as a whole. This, too, costs time and money in practice.
In documents DE 10 2008 025 725 A1 and DE 10 2008 027 890 A1, representing the current state of the art, it is the case in particular that no additional arrangement to protect the seal against axial expulsion is present on the side of the bearing on which the seal is fixed in a plunge cut. Assuming that the internal pressure of the bearing is too high due to lubricant, then a seal according to the two solutions just described is protected against axial expulsion only by the barb-shaped configuration of the seal in the plunge cut. In practice, this is far from adequate to guarantee reliable positional securement of the seal. Such a desirable type of securement does exist, to some extent, in WO 2010/043249 A1—referring, here, to an annular groove similar in shape to the sort of tongue and groove securing arrangement commonly used in sturdy types of construction—but it is far from sufficient to ensure reliable positional securement of the seal against axial expulsion due to excessive pressure from the center of the bearing.
What is actually needed, in the view of the practitioner, is a one-piece solution (fewer parts means faster installation, less complexity, etc.) that extends all the way around the rotary joint and is made from the conventional sealing materials—where appropriate, even a magnetizable or magnetic elastomeric material that remains very securely in the seal. In particular, the practitioner requires a sealing arrangement that is simply held firmly in the seal by virtue of the suitably rational configuration of the geometry of the bearing component. Ideally, not only is the seal held firmly, but its cross-sectional profile is designed such that with increasing pressure from the direction of the sealing space to be sealed, i.e., from the direction of the interior of the bearing, an increasing counterforce is also exerted that counteracts axial expulsion. The practitioner therefore requires a sealing solution which, in effect, “clings” to its location when the pressure from inside the bearing increases and threatens to push the seal out of the bearing.
Taking these disadvantages into account, the task that presents itself is to create a sealing arrangement that is as optimal as possible and offers the best possible positional stability. The uppermost goal is to create a low-cost, versatile and one-piece solution for sealing rolling bearings, slewing bearings, rotary joints, slew drives, etc. In particular, the seal should preferably be suitable for use in rotary joints of wind power installations.